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                <title>Identification - Formula prediction - RDBE restrictions</title>
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                <h1>Formula prediction - RDBE restrictions</h1>

                <h2>Description</h2>

                <p>
                The Ring Double Bond Equivalents (RDBE) value, which estimates the number of rings and
                unsaturated bonds in a molecule, can be calculated from a chemical formula using
                the following general equation:<br>
                <img src="rdbe_equation.png"><br>
                where n<sub>i</sub> is the number of atoms and ν<sub>i</sub> the formal valence of the element i.
                Theoretically, each ring or a double bond increases the RDBE value by 1,
                while each triple bond increases the value by 2.
                This equation can only be used for formulas composed of elements with a well-defined formal valence.
                </p>
                
                <p>
                A number of exceptions to the RDBE rule are known, however the RDBE value still provides
                a useful indicator regarding the validity of a molecular formula.
                </p>

                <h4>Method parameters</h4>
                <dl>
                        <dt>RDBE range</dt>
                        <dd>Range of allowed RDBE (Range or Double Bonds Equivalents) value.
                        Kind and Fiehn (BMC Bioinformatics, 2007) recommended the RDBE upper limit of 40 for common chemical compounds.
                        They also stated that RDBE should not be negative, although certain exceptions may occur when formal
                        valence states are exceeded. 
                        </dd>

                        <dt>RDBE must be an integer</dt>
                        <dd>Only integer values are allowed for RDBE. This condition is a natural implication 
                        of the principle of valence balance, which states that the number of atoms with odd
                        valence must be even. Such assumption is valid for all neutral,
                        non-radical molecules.
                        </dd>
                        
                </dl>

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